The experimental challenge under controlled laboratory conditions of patients with certain forms of physical urticaria--cold, cholinergic, and solar--provides an in vivo model of mast cell activation in humans. The specific aims of the study of the mediators of inflammation in such patients with physical urticaria are a continued definition and analysis of the released mast cell-derived products and an analysis of the morphologic alterations occurring in the skin. Blood will be analyzed for the appearance of histamine, factors chemotactic for neutrophils and eosinophils, and chemotactic responsiveness of peripheral blood leukocytes. The chemotactic activities will then be further characterized physicochemically and functionally with the objective of allowing comparative studies in these mast cell-dependent disorders. The study of patients with cholinergic urticaria with pulmonary manifestations offers the opportunity to assess the effects of endogenous mediator release on the airways. The evolution of the morphologic changes in skin biopsy specimens will be defined by 1-Mum, Epon-embedded tissue stained with Giemsa. This technique allows recognition of mast cells and basophils, differentiation among mononuclear cell types, and the observation of alterations in the cutaneous microvasculature. Thus, these human models synthesize observations of the evolution of clinical manifestations, histologic analysis of tissue alterations, measurement and characterization of mediators released into the circulation, and assessment of the effects of mediators on leukocyte motility. These human studies will be used to define immunopathologic mechanisms and may suggest therapeutic maneuvers.